Teletherapy is defined as a treatment methodology in which an irradiation source is at a distance from the body to be treated. X-rays and electron beams have long been used in teletherapy to treat various cancers. Unfortunately, X-rays exhibit a linear energy transfer approaching an exponential attenuation function, and are therefore of minimal safe use for deeply embedded growths. The use of heavy particles, particularly hadrons and more particularly protons, in teletherapy has found increasing acceptance, due to the ability of heavy particles to penetrate to a specific depth without appreciably harming intervening tissue. In particular, the linear energy transfer of hadrons exhibits an inversed depth profile with a marked Bragg peak defined as the point at which the hadrons deposit most of their energy, and occurs at the end of the hadrons path. As a result of this effect, increased energy can be directed at an embedded growth as compared to X-rays and electron beams, which particularly harm intervening tissues. While the term hadrons include a wide range of particles, practically, protons and various ions are most widely used in therapy. For clarity, this document will describe treatment as being accomplished with protons, however this is not meant to be limiting in any way.
The charged protons or ions can be focused to a target volume of variable penetration depth. In this way the dose profile can be matched closely to the target volume with a high precision. In order to ensure complete irradiation of the target growth, a plurality of beams arriving at the embedded growth from several different directions is preferred. The point at which the plurality of beams intersects, whether they are beamed sequentially or simultaneously, is termed the isocenter, and to maximize biological effectiveness the isocenter must be precisely collocated with the target growth.
The above is accomplished in the prior art by a gantry system carrying a beam generating and delivery system. Unfortunately, the beam generating and delivery system is extremely heavy, and the need for such a gantry system leads to a prohibitively expensive structure limiting the number of available proton therapy centers. Such a gantry system does however advantageously treat the entire range of patients, irrespective of required irradiation angle.
An alternative to gantry systems is a fixed beam irradiation source, wherein irradiation is provided from a fixed location charged hadron source with optional post beam generation scanning or scattering functionality. In addition, fixed beam irradiation is not limited to that from a single treatment irradiation source, but can include multiple fixed beams which are independently controlled or jointly controlled. The term fixed beam is thus differentiated from a gantry system in that the treatment beam source is fixed in relation to the walls, floor and ceiling of the treatment room and is not generally movable.
It is to be noted that patient treatment for irradiation may be broadly broken into 2 groups: patients treated in a supine, prone and similar positions, also known as a horizontal treatment position; and patients treated in a seated or standing position, also known as a vertical treatment position. It is to be understood that the terms horizontal treatment and vertical treatment are not strictly limiting, and a range of angles about the strictly horizontal and the strictly vertical are included in each of the respective treatment positions. In particular, inclined treatment may be provided by either an inclination from the horizontal position or from the vertical position. Alternately, the beam may be inclined while the patient is in one of the horizontal and vertical positions.
Irradiation treatment is performed on a target tissue in a well defined process. In a first stage, known as the treatment planning stage, the target tissue is imaged and a treatment plan comprising dosage, patient position, and irradiation angles are defined. Furthermore, placement markers are defined, so as to ensure that subsequent irradiation sessions are properly targeted. Irradiation is then performed, responsive to the developed treatment plan, at a plurality of treatment sessions over a period of time, each session being known as a fraction. At each such fraction, care must be taken to ensure proper patient positioning, responsive to the placement markers, so as to avoid damage to organs in vicinity of the target tissue. Positioning of the patient responsive to the markers is performed based on visualization of the patient, responsive to the defined markers. Imaging performed with 3D imaging equipment, which according to the prior art is constituted of a CT scanner, advantageously may be used to both monitor the patient position compliant with the existing treatment plan and to determine validity of the existing treatment plan, since the CT scanner provides volumetric information to enable monitoring of anatomical changes within the target tissue. As a result, adjustment to the treatment plan may be performed responsive to the monitored anatomical changes within the target tissue.
U.S. Pat. No. 5,851,182 issued Dec. 22, 1998 to Sahadevan, the entire contents of which is incorporated herein by reference, is addressed to a patient setup and treatment verification system for radiation therapy having diagnostic imaging devices connected to a room containing a megavoltage radiation therapy machine. Daily patient setup for routine and three-dimensional conformal radiation therapy and on-line treatment port verification with superimposed isodose are done with a patient on a diagnostic imaging table. The patients are transferred from the diagnostic imaging table to the treatment table without changing the verified treatment position. Such a system is limited to a patient being treated in a supine position, thus requiring a costly gantry based irradiation system.
U.S. Pat. No. 7,847,275 issued Dec. 7, 2010 to Lifshitz et al., the entire contents of which is incorporated herein by reference, is addressed to a patient treatment arrangement comprising: a treatment irradiation source; and a patient positioning mechanism in communication with a patient support surface and operative to achieve positioning of the support surface equivalent to rotation of the patient support surface of at least 180° about any one of three orthogonal axes and translation of the patient support surface along any of three orthogonal axes. In addition an imager is provided arranged to image a target tissue at the irradiation angle. Such an imager adds cost to each treatment room, since commercially available imagers are primarily arranged to image patients in a fixed, predetermined position, generally horizontal.
U.S. Pat. No. 7,796,730 issued Sep. 14, 2010 to Marash et al., the entire contents of which is incorporated herein by reference, is addressed to an irradiation treatment apparatus comprising an imager arranged for vertical translation of a patient. Such an apparatus is ideal for vertical translation, however is not particularly appropriate for generally horizontal patient treatment positions.
There is thus a long felt need for an improved treatment arrangement which improves patient throughput by being usable for both horizontal treatment positions and vertical treatment positions.